In optical communication, there has been used an apparatus such as an optical receiver for receiving optical signals and converting them into electrical signals, an optical transmitter for converting electrical signals into optical signals and transmitting the optical signals, or an optical transceiver formed by integrating the optical receiver with the optical transmitter to reduce the size and cost thereof. For example, refer to Japanese Laid-open Patent Publication No. 2009-232380. It has been known a monitoring circuit used in the optical transceiver which monitors a current flowing in a optical receiving element corresponding to an optical signal received by the optical receiver, which is disclosed in, for example, Japanese Laid-open Patent Publication No. 2003-198279.
An optical interconnect has attracted attention for an optical data transmission over a relative short distance in a supercomputer, server, or the like. The optical interconnect is used for a line between computers, boards, chips mounted on a board, elements included in a chip, or the like. A data rate of the signal propagated through the optical interconnect has increased over the years and is expected to increase, for example, 25 Gb/s or higher in the future. For example, it is found in “InfiniBand Roadmap” published on the web, URL: http://www.infinibandta.org/content/pages.php?pg=technology_overview, searched on Jan. 4, 2011.
The optical communication is more resistant to electromagnetic noise than electrical communication and thereby there is less interference in a transmission path than the electrical communication. Accordingly the optical interconnect adopts an optical transmission line array that has a plurality of optical transmission lines arranged at narrow pitches of 0.25 mm, for example, to reduce the size of a wiring. A wiring connection or a flip-chip connection is used for each connection between optical element, such as a light emitting element or a light receiving element, and an electric circuit.